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From: "fcollyer at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug malloc/15592] New: mtrace.c tr_break() is not called from malloc hooks
Date: Thu, 06 Jun 2013 16:53:00 -0000
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http://sourceware.org/bugzilla/show_bug.cgi?id=15592

            Bug ID: 15592
           Summary: mtrace.c tr_break() is not called from malloc hooks
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: malloc
          Assignee: unassigned at sourceware dot org
          Reporter: fcollyer at gmail dot com

Looking at some dumps generated on a CentOS 5.6, it seems as if gcc is
optimizing away some calls to tr_break().

Everything is in place (according to the file instructions), but tr_break() is
not firing after setting its breakpoint.

Small gdb disasm from glibc-2.5x:

Dump of assembler code for function tr_freehook:
0x0066ffc0 <tr_freehook+0>:     push   %ebp
0x0066ffc1 <tr_freehook+1>:     mov    %esp,%ebp
0x0066ffc3 <tr_freehook+3>:     sub    $0x18,%esp
0x0066ffc6 <tr_freehook+6>:     mov    0x8(%ebp),%eax
0x0066ffc9 <tr_freehook+9>:     mov    %ebx,-0xc(%ebp)
0x0066ffcc <tr_freehook+12>:    call   0x616ce0 <__i686.get_pc_thunk.bx>
0x0066ffd1 <tr_freehook+17>:    add    $0xd3023,%ebx
0x0066ffd7 <tr_freehook+23>:    mov    %esi,-0x8(%ebp)
0x0066ffda <tr_freehook+26>:    test   %eax,%eax
0x0066ffdc <tr_freehook+28>:    mov    %edi,-0x4(%ebp)
0x0066ffdf <tr_freehook+31>:    je     0x6700a4 <tr_freehook+228>
0x0066ffe5 <tr_freehook+37>:    xor    %edi,%edi
0x0066ffe7 <tr_freehook+39>:    mov    $0x1,%esi
0x0066ffec <tr_freehook+44>:    mov    %edi,%eax
0x0066ffee <tr_freehook+46>:    mov    %esi,%ecx
0x0066fff0 <tr_freehook+48>:    cmpl   $0x0,%gs:0xc
0x0066fff8 <tr_freehook+56>:    je     0x66fffb <tr_freehook+59>
0x0066fffa <tr_freehook+58>:    lock cmpxchg %ecx,0x1648(%ebx)
0x00670002 <tr_freehook+66>:    jne    0x67040c <_L_lock_464>
0x00670008 <tr_freehook+72>:    mov    0xc(%ebp),%eax
0x0067000b <tr_freehook+75>:    call   0x66fe70 <tr_where>
0x00670010 <tr_freehook+80>:    mov    0x8(%ebp),%eax
0x00670013 <tr_freehook+83>:    mov    %eax,0x8(%esp)
0x00670017 <tr_freehook+87>:    lea    -0x1b2a9(%ebx),%eax
0x0067001d <tr_freehook+93>:    mov    %eax,0x4(%esp)
0x00670021 <tr_freehook+97>:    mov    0x1640(%ebx),%eax
0x00670027 <tr_freehook+103>:   mov    %eax,(%esp)
0x0067002a <tr_freehook+106>:   call   0x646e20 <fprintf>
0x0067002f <tr_freehook+111>:   cmpl   $0x0,%gs:0xc
0x00670037 <tr_freehook+119>:   je     0x67003a <tr_freehook+122>
0x00670039 <tr_freehook+121>:   lock subl $0x1,0x1648(%ebx)
0x00670041 <tr_freehook+129>:   jne    0x67041c <_L_unlock_481>
---Type <return> to continue, or q <return> to quit---
0x00670047 <tr_freehook+135>:   mov    %edi,%eax
0x00670049 <tr_freehook+137>:   mov    %esi,%ecx
0x0067004b <tr_freehook+139>:   cmpl   $0x0,%gs:0xc
0x00670053 <tr_freehook+147>:   je     0x670056 <tr_freehook+150>
0x00670055 <tr_freehook+149>:   lock cmpxchg %ecx,0x1648(%ebx)
0x0067005d <tr_freehook+157>:   jne    0x67042c <_L_lock_490>
0x00670063 <tr_freehook+163>:   mov    0x164c(%ebx),%eax
0x00670069 <tr_freehook+169>:   mov    -0x38(%ebx),%esi
0x0067006f <tr_freehook+175>:   test   %eax,%eax
0x00670071 <tr_freehook+177>:   mov    %eax,(%esi)
0x00670073 <tr_freehook+179>:   je     0x6700b1 <tr_freehook+241>
0x00670075 <tr_freehook+181>:   mov    0xc(%ebp),%edx
0x00670078 <tr_freehook+184>:   mov    %edx,0x4(%esp)
0x0067007c <tr_freehook+188>:   mov    0x8(%ebp),%edx
0x0067007f <tr_freehook+191>:   mov    %edx,(%esp)
0x00670082 <tr_freehook+194>:   call   *%eax
0x00670084 <tr_freehook+196>:   lea    -0xd3034(%ebx),%eax
0x0067008a <tr_freehook+202>:   mov    %eax,(%esi)
0x0067008c <tr_freehook+204>:   cmpl   $0x0,%gs:0xc
0x00670094 <tr_freehook+212>:   je     0x670097 <tr_freehook+215>
0x00670096 <tr_freehook+214>:   lock subl $0x1,0x1648(%ebx)
0x0067009e <tr_freehook+222>:   jne    0x67043c <_L_unlock_517>
0x006700a4 <tr_freehook+228>:   mov    -0xc(%ebp),%ebx
0x006700a7 <tr_freehook+231>:   mov    -0x8(%ebp),%esi
0x006700aa <tr_freehook+234>:   mov    -0x4(%ebp),%edi
0x006700ad <tr_freehook+237>:   mov    %ebp,%esp
0x006700af <tr_freehook+239>:   pop    %ebp
0x006700b0 <tr_freehook+240>:   ret
0x006700b1 <tr_freehook+241>:   mov    0x8(%ebp),%eax
0x006700b4 <tr_freehook+244>:   mov    %eax,(%esp)
0x006700b7 <tr_freehook+247>:   call   0x66a990 <free>
0x006700bc <tr_freehook+252>:   jmp    0x670084 <tr_freehook+196>
End of assembler dump.

This can be mapped to the corresponding source-code:

http://sourceware.org/git/?p=glibc.git;a=blob;f=malloc/mtrace.c;h=1a9522b09de37f96fb9e4ed807f3cc1dedaca3fb;hb=88cc61e84e8e75e6e91b1a2e51147aeb63712ff8

146   tr_where (caller);
147   /* Be sure to print it first.  */
148   fprintf (mallstream, "- %p\n", ptr);
149   __libc_lock_unlock (lock);
150   if (ptr == mallwatch)
151     tr_break ();
152   __libc_lock_lock (lock);

Inlined gcc tls lock code around tr_break() seems to be ok.
tr_break() related code seems to be missing.

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